2. amps-preamps
  3. 1301660135

KT120 Tube compatibility w/ Jadis Defy 7 Amp MK 1

Hi, I have an original Jadis Defy I just acquired for I liked its sound very much. However, I don't have any users manual or schematic for the serial #445. Could anyone help by sending a .pdf or electronic copy.

Also, there is a new tube out for the KT88/6550/KT90/EL34 socket line called the KT120. It is the most powerful tube of all of them.

I would like to replace all of the current (12) 6550B tubes with the new larger KT-120 Tubes by Tung Sol (which has a plate dissipation of 60 watts, making it the most powerful tube in the 6550/KT88/KT90 family, or approximately 10 more watts/tube vs. KT90 . Also, when used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT120 is impervious to overload, delivering peak power with extreme reliability and long tube life). Another note regarding universal replacement/compatibility is that the glass envelope of the KT-120 tube is 1/2" taller than other KT88 cousins to accommodate the larger internal plate structure and larger control grid cooling fins, which won't present a problem. However, a word of caution is given regarding the KT120's small increase in current vs. the next most powerful KT88 or KT90 (close in current draw), wherein they say the filament of this tube draws 1.7A to 1.95A, or 0.1 Amp to 0.35 Amp (100 to 350 mA) more current than a KT88 at 1.6 amp; so they say to be safe and recommended to check with your amp manufacturer to make sure the Jadis Defy 7 filament transformer will or can handle the increase in current (at 0.1 to 0 .35A/tube and if you have a quad that is 0.4-1.4A total additional current draw with normal current of 1.6A/tube) without any transformer mods. Will this small increase in current for the Jadis Defy 7 filament transformer be able to handle this increase draw in current required of the Tung-Sol JT120?

Any help answering this technical question would be greatly appreciated and I would gladly pay for a owners manual/schematic for this 100wpc push-pull configured amp design.
bradleys

Showing 2 responses by rwwear

rwwear
2,847 posts
 
Bob Carver told me this when I told him I was afraid I would damage the power transformer using KT 120's in my Citation II:

The KT120s are larger, more powerful tubes and pull down about an extra 40 volts. That allows substantially more power. It is true that the KT120s require more filament power, but not enough to even begin overloading the power transformer, especially since you will not increase the plate current at all. Actually you will bias the '120s at a LOWER current than the '88s, and the output transformer will run COOLER than it is now with '88s. Hope this helps,
Bob
rwwear
2,847 posts
 
Good question Geek. He seems to have a lot of experience in the subject since he owns many Citations and designed his new tube amps around the Citation V. It uses KT 120s.
Carver Amps
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